‘Merbeingold 2336’ is a new variety of mandarin (Citrus species) bred by CSIRO Plant Industry. A copending application, U.S. Ser. No. 11/729,049, has been made for the variety ‘Merbeingold 2350’, which is a sibling selected from the same family as ‘Merbeingold 2336’.
‘Merbeingold 2336’ is a mandarin variety selected from a family produced by making a controlled cross between ‘Imperial’ mandarin (seed parent) with ‘Ellendale’ tangor (pollen parent). Thus, the botanical name for the plant is:
Citrus reticulata×(C. reticulata×C. sinensis)
The plant was asexually reproduced in South Australia, Australia.
‘Merbeingold 2336’ was selected from a family of 241 hybrids generated by a controlled cross-pollination of ‘Imperial’ mandarin (maternal parent) with ‘Ellendale’ tangor (pollen parent).
‘Imperial’ mandarin (unpatented) is an Australian variety that originated at Emu Plains, NSW, as a chance seedling in 1890. It is possibly a hybrid of the ‘Mediterranean’ mandarin. ‘Imperial’ trees are vigorous, upright and of medium size and they yield fruits that are early maturing.
‘Ellendale’ tangor (unpatented) is another Australian variety that was discovered as a chance seedling at Burrum, Queensland in 1878. Although its parentage is unknown, its characteristics and fruit size indicate that it is a tangor (mandarin×orange cross). ‘Ellendale’ trees are generally large and of a spreading-round habit and produce large mid-to-late season fruit depending on where they are grown.
The seediness of fruits from both ‘Imperial’ and ‘Ellendale’ can be variable ranging from many-to-few-to-zero depending on the proximity of other sources of pollen. Both varieties are capable of producing fruits parthenocarpically.
CSIRO Plant Industry crossed ‘Imperial’ with ‘Ellendale’ to combine the characteristics of the two varieties and generate new parthenocarpic hybrids for selection of potential new varieties of seedless mandarins.
The controlled cross-pollination was conducted by emasculating an un-opened flower bud of the maternal parent and applying pollen from the paternal parent to the receptive stigma using a sterile soft-haired paintbrush. Pollen of ‘Ellendale’ tangor was collected by drying anthers, which had been removed from unopened flower buds, in Petri dishes over silica gel in a dessicator. Dried dehisced anthers were stored in sealed glass vials over silica gel at 4° C. until needed. The cross was made in 1984 and the resultant seeds were extracted from fruits in 1985 and sown in a standard seed bed under glasshouse conditions. Emergent seedlings were transferred to a standard potting mix in pots and maintained under glasshouse conditions until they were rowed out in the breeding orchard at a planting density of 2 m within and 6 m between rows. Hybrid seedlings were maintained under irrigated orchard conditions thereafter. Standard citrus cultivation techniques were used to maintain the trees including application of fertilisers.
When hybrid 2336 flowered, it was subjected to a range of pollination treatments to assess its potential for producing seedless fruits. Fruits were harvested over 4 years and assessed for fruit quality, Based on the data collected, hybrid 2336 was selected for entry into second phase evaluation trials.
The selection was entered into a comparative trial at CSIRO Plant Industry Koorlong (NW Victoria). Trees of hybrid 2336 and 4 comparator varieties (viz. ‘Clementine Nules’, ‘Imperial’ mandarin, ‘Ellendale’ tangor, and ‘Merbeingold 2350’) were propagated by budding to 3 rootstocks (viz. ‘Carrizo’ citrange, ‘Cleopatra’ mandarin and ‘Symons’ sweet orange) in the nursery at CSIRO. The DUS trial was planted during spring 2001. The soil type was classified as being Tiltao sand (Northcote, K.H. 1951. A Pedological Study of the Soils Occurring at Coomealla, New South Wales, Commonwealth Scientific and Industrial Research Organisation, Melbourne, Australia). The trees were irrigated by overhead sprays and fertilised using a standard citrus N:P:K (12:3:3) formulation. Fertiliser was applied to young trees at 2-monthly intervals and to trees 2 years and older at six-monthly intervals at a rate such that they received 800 kg/ha/year. Trace elements, primarily manganese and zinc were applied as foliar sprays as required. The trial was embedded within a larger trial that compared other selections from CSIRO's citrus breeding program. The trial was laid out as two randomized blocks with a three-tree plot for every scion/rootstock combination within each block. Rootstocks were randomized within plots. Trees were maintained vegetatively for the first three years and allowed to retain fruits from season 2004-05 onwards.
Comparative data for quantitative fruit characteristics were collected in seasons 2006 and 2007. Spring-flush leaves were sampled from trees during January 2007.
Hybrid 2336 was also entered along with other selections into regional test plots with anonymous cooperating citrus growers under confidential testing agreement arrangements to protect inherent intellectual property. Based on its performance in these trials and test plots, hybrid 2336 was named ‘Merbeingold 2336’.
Daughter trees of ‘Merbeingold 2336’ propagated from the original seedling tree by asexual or vegetative means are uniform and stable. Similarly grand-daughter trees are uniform and stable. Trees of ‘Merbeingold 2336’ have been propagated by grafting or budding to seedling rootstocks, by top-working to established orchard trees and by rooting cuttings, confirming its uniformity and stability.